WCAG: Review fixes - arrow keys, PageTab roles, AlertMessage

Add Up/Down arrow key navigation to Settings sidebar.
Add Accessible.role: Accessible.PageTab to all 5 tab pages.
Fix Loader status to use AlertMessage role per WCAG 4.1.3.

src/ui/qml/Loader.qml

@@ -161,7 +161,7 @@ ApplicationWindow {
                     font.family: jetBrainsMono.name
                     font.pixelSize: 11
                     font.bold: true
-                    Accessible.role: Accessible.StaticText
+                    Accessible.role: Accessible.AlertMessage
                     Accessible.name: "Loading status: " + text
                     anchors.horizontalCenter: parent.horizontalCenter
                     opacity: 1.0

src/ui/qml/Overlay.qml

@@ -282,7 +282,7 @@ ApplicationWindow {
                 radius: width / 2
                 color: "transparent"
                 border.width: 2
-                border.color: "#B794F6"
+                border.color: "#B794F6" // SettingsStyle.accent equivalent
                 visible: micContainer.activeFocus
             }
         }

src/ui/qml/Settings.qml

@@ -226,6 +226,18 @@ Window {
                             Accessible.role: Accessible.Tab
                             Keys.onReturnPressed: stack.currentIndex = index
                             Keys.onSpacePressed: stack.currentIndex = index
+                            Keys.onDownPressed: {
+                                if (index < navModel.count - 1) {
+                                    var nextItem = navBtnRoot.parent.children[index + 2]
+                                    if (nextItem && nextItem.forceActiveFocus) nextItem.forceActiveFocus()
+                                }
+                            }
+                            Keys.onUpPressed: {
+                                if (index > 0) {
+                                    var prevItem = navBtnRoot.parent.children[index]
+                                    if (prevItem && prevItem.forceActiveFocus) prevItem.forceActiveFocus()
+                                }
+                            }
 
                             Behavior on color { ColorAnimation { duration: 150 } }
 
@@ -315,6 +327,7 @@ Window {
                     
                     // --- TAB: GENERAL ---
                     ScrollView {
+                        Accessible.role: Accessible.PageTab
                         ScrollBar.vertical.policy: ScrollBar.AsNeeded
                         contentWidth: availableWidth
                         
@@ -412,6 +425,7 @@ Window {
 
                     // --- TAB: AUDIO ---
                     ScrollView {
+                        Accessible.role: Accessible.PageTab
                         ScrollBar.vertical.policy: ScrollBar.AsNeeded
                         contentWidth: availableWidth
                         
@@ -500,6 +514,7 @@ Window {
 
                     // --- TAB: VISUALS ---
                     ScrollView {
+                        Accessible.role: Accessible.PageTab
                         ScrollBar.vertical.policy: ScrollBar.AsNeeded
                         contentWidth: availableWidth
                         
@@ -618,6 +633,7 @@ Window {
 
                     // --- TAB: AI ENGINE ---
                     ScrollView {
+                        Accessible.role: Accessible.PageTab
                         ScrollBar.vertical.policy: ScrollBar.AsNeeded
                         contentWidth: availableWidth
                         
@@ -1078,6 +1094,7 @@ Window {
 
                     // --- TAB: DEBUG ---
                     ScrollView {
+                        Accessible.role: Accessible.PageTab
                         ScrollBar.vertical.policy: ScrollBar.AsNeeded
                         contentWidth: availableWidth